JPS58147676A - Nuclear fuel element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in nuclear fuel elements for nuclear reactors.

Figure 1 shows a cross-sectional view of a typical nuclear fuel element used in a nuclear reactor, 1 is a nuclear fuel element, and nuclear fuel 4I cable 1 is:
It is formed of a cladding tube 2 which contains a large number of stacked fuel pellets 3 made of sintered carbon dioxide (UOt) and is welded and sealed at the upper and lower ends with an upper end plug 4 and a lower end plug 5. Inside the nuclear fuel element l, there is a gap gas with a thermal conductivity of φ.
- A gas plenum 6 is provided at the top to prevent pressure rise within the nuclear fuel element 1 due to the fission product gas released from the fuel pellet 3. A coil spring 7 is disposed within the gas plenum 6 and holds down the fuel pellet 3 so that it does not move up and down within the cladding tube 2 during nuclear fuel transportation. Further, a moisture getter 8 made of nickel and teta/I zirconium is placed inside the coil 1t27,
Stones are designed to absorb water S and moisture that are absorbed during the production of fuel pellets and released during the early stages of reactor operation.

Atomic fOf mind, nuclear fuel like this! ! Multiple element I
When a large number of nuclear fuel assemblies arranged in the IL period are installed and the reactor is started, the heating fuel pellet 8 has a temperature close to that of the paraboloid 11, and the fuel pellet The fuel pellets 3 are deformed into a chain shape and cracks occur in the fuel pellets 3 due to thermal stress, and the fuel pellets 3 are rearranged and the gap between the fuel pellets 3 and the cladding tube 2 is eroded.

When the output t of the nuclear fuel element 1 is further increased, the fuel pellet 3 and the cladding tube 2 come into contact with each other due to the thermal expansion of the fuel pellet 30, and a mechanical interaction occurs.

On the other hand, fission products of 21111i1 are generated by 1HO1 & fission, and about α3 of the fission products are gaseous OIm fission products, and on the other hand, corrosive fission products g*x
The lukewarm iodine is one of the nuclear fuel elements l roaring 111j1
Approximately 20-30mgmg per 1:100100O/T
be done. In this way, the ls* nuclear fission product gas Wt accumulated together with the combustion of the fuel pellet 3 causes stress corrosion cracking failure of the fuel pellet 3 and the cladding tube 2 described above. This nuclear fuel 1! The degree of sulfuric acid required to cause stress corrosion cracking gIL loss of $1 is 3% relative to the surface area of the cladding tube.
X I O-'g/cxx", the tensile stress of the cladding tube 2 due to the fuel pellet 3 is 20 GMP, and if the iodine is less than this, or the tensile stress of the cladding tube 2 due to the fuel pellet 3 is the stress of the nuclear fuel element, l. It is said that corrosion cracking failure does not occur. However, once stress corrosion cracking failure occurs in the nuclear fuel element 1, contact between the fuel pellet 3, which serves as the cladding tube 2, and the cooling water and chemical reaction are prevented. This impairs the avA, which prevents the radioactive fission products released from the fuel pellet 3 from entering the cooling water, and increases the radioactivity level in the cooling facility.

The damaged FE nuclear fuel element 1 not only contaminates the cooling water with radioactive fission production, but also stops the atomic F to prevent the spread of cooling water contamination and transfers the nuclear fuel assembly containing the damaged nuclear fuel element It to the reactor. It is necessary to take out the fuel from the reactor, reducing the operating rate of the reactor and reducing the economic loss of the core fuel prefecture.

The ninth step to prevent damage to the nuclear fuel element 1 due to ζO stress corrosion cracking is to prevent mechanical interaction between the fuel pellet 3 and the cladding tube 2, or to expose the Zircal cladding tube 1 to corrosive fission product gas. There is a need to prevent eels more than anything else. Therefore, in order to remove harmful elements in the nuclear fuel element 1 and protect the cladding tube 2 from corrosive fission gases, an iodine getter that easily reacts chemically with iodine in the Zircaloy cladding tube 2 is added to the nuclear fuel element.
A box is being considered in which a metal layer is provided between the fuel pellet 3 and the cladding tube 2 to create a barrier between the iodine and the cladding tube 2. However, with the iodine getter, it is difficult to deal with the sudden change in the concentration of the nuclear fuel due to the release of the nuclear cloud formation gas that has been accumulated in the fuel pellet 3 due to a significant increase in the output of the nuclear fuel element 10. φ
However, the barrier material and the gk material inside the cladding have a large neutron absorption cross section, which reduces neutron economics and reduces nuclear fuel 11) 1! The disadvantage is that it increases the manufacturing cost of the element. The oxide film on the inner surface of the Zircaloy cladding tube 1 can serve as a strong protection film against iodine, which is a corrosive fission product gas.

The bottom surface of the cladding tube of existing nuclear fuel elements is coated with an oxide film of several microns in advance during the manufacturing process, but the oxide film is damaged due to mechanical interaction between the fuel pellet 3 and the cladding tube 2 during irradiation. There is a possibility that it will be attached. It is said that when VceIR elementary gas is present in the gas atmosphere within the nuclear fuel element 1, the Zircaloy cladding tube 2 is more likely to undergo an oxidation reaction faster than iodine. And, it is impossible to encapsulate 112 elements in nuclear fuel element 1 from the beginning.53-14049
This was already discussed in Publication No. 3, and it was also considered that the cost of nine nuclear fuels would increase by including an oxide that reacts with the compound and releases acid X.

However, in the conventional nuclear fuel element X1 in which the M gas is sealed in the nuclear fuel element l from the beginning, heat conduction of the gap gas between the fuel pellet 3 and the cladding tube 2 due to the mixing of oxygen gas. This leads to a decrease in the fuel pellet 3, resulting in a m degree rise in the fuel pellet 3, a worsening of the mechanical interaction between the fuel pellet 3 and the cladding tube 2 due to an increase in the amount of thermal expansion, and an increase in the amount of fission product gas released from the fuel pellet 3. Leads to environmental stratification. And reactor luck @O
Nickel and titanium also for the nine water getter placed within the nuclear fuel element l to absorb the hydrogen and moisture initially released from the fuel pellet 3.

The moisture getter material made of the Zirpnicum alloy reacts with oxygen, resulting in a decrease in the total absorption capacity of the moisture getter material for hydrogen and moisture.Also, even if an oxide is placed in the nuclear fuel element, the output of the nuclear fuel element 1 will be significantly reduced. There is a drawback that it is not possible to cope with sudden deterioration of the forest condition due to the release of a large amount of iodine from the fuel pellet due to increased Jl.

The present invention was made in view of the above situation, and an object of the present invention is to provide a nuclear fuel element that can prevent damage due to stress corrosion cracking of the cladding tube and improve the safety and effective operability of a nuclear reactor. It is something.

The nuclear fuel element of this shield Ijli consists of a fuel pellet enclosed and sealed in a temporary stack tube, a stress corrosion cracking suppressing gas sealed in a gas brenum inside the upper end of the cladding tube, and nuclear fission generation in the above-mentioned fuel sleeve. Nine capsules are built in to release the stress corrosion cracking suppressing gas based on the pressure difference between the gas and the internal pressure of the temporary tube.

The following is one example of the nuclear fuel element of the present invention, 1fA? The same parts as in the conventional Il are indicated by the same reference numerals, and the explanation of the same parts is omitted in Fig. s2.

This will be explained with reference to FIG. FIG. 2 is a longitudinal sectional view of the nuclear fuel element, and FIG. 3 is a longitudinal sectional view of the oxygen-filled capsule of FIG. The nuclear fuel element 1 is coated with Zircaloy-2 and has an inner diameter of 10.8 cm, a wall thickness of α86 m, and a total length of 4 m. ni1α5
A 6m long U Os fuel pellet 3 was loaded over a length of 6m, and 1 atm of helium gas was filled in. After death, both the upper and lower ends t
Welded can *i is fitted with m stopper 4.5. Inside the plenum 6 are a coil spring 7, a moisture getter 8 and an I! IX enclosed capsule 9 is stored. Nariki enclosed capsule 9 is the third
As shown in the figure, the outer diameter is 6 cm, the wall thickness is α2 cm, and the length is 2 cm.
0■ Zircaloy tube 10, a Zircaloy thin film 11 with a thickness α05- formed on one end of the tube lO, and a thin 11
[1ml on 11! A ventrator 12 is formed to release a large amount of money by utilizing the pressure difference between the element-sealed capsule 9 and the nuclear fuel element l, and the oxygen gas 13 at positive pressure sealed inside.
It consists of The thickness of the thin film 110 is 1/'113 because stress corrosion cracking occurs due to oxidation in the gap gas of iodine, which is a corrosive fission product gas.
When the size is smaller than 2.5 x 10''' and 117ex'', the thin j [
It is shaped so that a hole is made by the pressure applied to 11 and the sharp needle tip of venetrator 12.

When the nuclear fuel element is installed in the reactor and the reactor starts operating, the temperature of the fuel pellet 3, that is, the nuclear fuel 1! Determined by the output of XI and Sat. Threshold 1 of iodine in gap gas causing stress corrosion cracking failure [3X10-g/aII
W#O maple fuel element 10 burnup reaching oz s x 1o -'g/cm'
When operated at a constant output of 4N) W/am, approximately 100
00 MWD/ Two, and also 400 W/
Operating at a constant output of cI11, approximately 3000MW
D/Tυ-. At this time, the pressure outside the oxygen-filled capsule 9 was increased, and the thin film 11 was broken by the ventrator 12, and the I sealed inside the oxygen-filled capsule 9 was
I! The elementary gas 13 is released into the nuclear fuel element 1, creating a safe gas atmosphere ([8 Torr or more in the gas plenum 6]) that can prevent stress corrosion cracking damage due to iodine, which is a corrosive fission product gas, and the nuclear fuel Stress corrosion cracking failure of element 1 can be prevented.

FIG. 4 shows another embodiment, in which the thin J of the penetration-resistant capsule 9 is
[In order to easily break 11, helium gas 15t- is sealed in the bellows 14 at a pressure higher than that of the rR industrial gas 13, the nuclear fuel element 1 is installed in the reactor, and the reactor is operated ( Cooling water temperature: 280U) When the penetrator 12 starts cooling, the thin film 1 due to the increase in the internal pressure of the bellows 14
An oxygen-filled capsule 9 can also be used which applies force to the oxygen-filled capsule 9 and is ruptured by the penetrator 12 when the pressure outside the oxygen-filled capsule 9 increases. Also, the thickness t of the thin film 11
Oxygen-filled capsules 9 of different orders are placed in the gas plenum 6 of the nuclear fuel element 1, and the difference in the internal pressure of the nuclear fuel element 10 is
Therefore, the thin film 11 may be sequentially torn at different points of death.

In both of the above-mentioned investigations, we have discussed cases in which oxygen is used to suppress stress corrosion cracking of nuclear fuel elements due to corrosive fission product gases, such as crystals.
Water vapor and nitrogen have similar effects on young fruits. Even if these hydrogen, water vapor, and base materials are sealed in a carburetor as a substitute for the dense mixed gas t1-related materials,! II! Similar to raw gas, it can prevent stress corrosion cracking and damage in the fuel tank.

As described above, the nuclear fuel element of the present invention can prevent damage due to stress corrosion cracking and has atomic F(Z) safety.

9a Improved drivability [improvement has a significant effect of t-1.

[Brief explanation of the drawing]

Figure s1 is a longitudinal view of a conventional nuclear fuel element, and Figure 2 is the nuclear fuel of the present invention! ! 3 is a detailed view of the oxygen-filled capsule of FIG. 2, and FIG. 4 is a 1JtX-filled capsule of the same part as in FIG. 3 of another example of the nuclear fuel element of the present invention. FIG. 1...Nuclear fuel element, 2...41.6I tube, 3...
Fuel pellet, 6... Gas plenum, 9... Oxygen capsule, 13 Fig. 1 Fig. 2

Claims (1)

[Claims] 1. In a reef fuel element in which fuel pellets are sealed and sealed in a cladding tube, a stress corrosion cracking suppressing gas is sealed in a gas plenum inside the upper end of the temporary cladding tube, and a stress corrosion cracking suppressing gas is sealed in the nuclear fuel element. Based on the nuclear fission product gas (the nuclear fuel element characterized in that it has a built-in capsule formed to release the stress corrosion cracking suppressing gas based on the pressure difference between the internal pressure of the cladding tube and the internal pressure of the nuclear fission product). The cut fuel element according to claim 1, wherein the capsule is sealed with a stress corrosion cracking inhibiting gas of 111 or more of oxygen, hydrogen, III hydrogen, and water vapor. 3. The stress corrosion cracking suppressing gas in the gas plenum Crack-suppressing gas [thin metal O formed so as to break when released nuclear fuel elements.